Access the x, y, z, w components using [0], [1], [2], [3] respectively.

	var p : Quaternion;
	p[3] = 0.5; // the same as p.w = 0.5

using UnityEngine;
using System.Collections;

public class Example : MonoBehaviour {
    public Quaternion p;
    void Example() {
        p[3] = 0.5F;
    }
}

import UnityEngine
import System.Collections

public class Example(MonoBehaviour):

	public p as Quaternion

	def Example() as void:
		p[3] = 0.5F